It should be noted here that the cost structure of insurance is pretty well known, and accessible to most any actuary or other statistically trained person. You have about 2% overall profit by insurance companies, between 10-20% overhead costs, and the rest goes to the care providers. So how do you get to costs up to 29% below expectations?

Simple. Each insurance company has a payment percentage. If you look at your healthcare bills, you'll see the initial number, an insurance discount, and then the amount you and your insurer finally pay. So to get to 29% less than the prediction, you simply assume that a certain portion of doctors will need to take a lot less for their services to keep working.

Translated, this means that a lot of Californians are likely to learn the hard way that having health insurance is not the same as having healthcare.

Update: it turns out that California's overall "reduction" in health insurance premiums actually turns out to be an increase of 64% to 146% when one compares the premiums for their plan with the actual peer group of insurance plans from the individual market instead of highly regulated corporate plans.